Tim Southee's remarkable all-round onslaught against Wellington at Karori Park won't even be the highlight of his week.

The New Zealand fast bowler blasted his maiden first-class century then ripped through Wellington's top order yesterday but the bubbly will remain on ice until Friday.

That's when Southee's partner, Alice, is due to be induced to give birth to their son before dad departs for the two tests against South Africa.

"It's been a crazy few months but it's exciting times," said Southee, who turned 24 last week.

Not so much for the Firebirds, who were graced by Southee's presence for Northern Districts only when he was unavailable for the three-match Twenty20 series in South Africa, starting on Saturday, due to the impending birth.

At stumps on day one of the Plunket Shield match, Wellington were staggering at 32-4 in reply to ND's 403-8 declared. Southee had all the scalps, 4-16 in a slick five-over spell in the gathering gloom.

Already established as New Zealand's No 1 strike bowler, Southee hopes to add "all-rounder" to his description, having broken through for an overdue ton in his 48th first-class match.

Striding to the crease at 161-6 on another good batting surface, Southee let rip to score 156 off 130 balls, including 18 fours and six sixes. Wellington's bowling attack, without injured trio Mark Gillespie, Andy McKay and Chris Woakes, slumped their shoulders and watched the Kookaburra fly to all parts after removing test batsmen Daniel Flynn, Kane Williamson and B J Watling relatively cheaply.

Southee's previous best first-class innings was 77 not out on test debut against England at Napier in 2008.

"In the past I haven't really given myself a chance. I've done something silly early in my innings. Today I thought I'd just bat and play each ball on its merit." Southee said.

"It's been a while. It's only one innings but I have worked reasonably hard on my batting in the last 12 months."

He hopes there's more to come in South Africa where he'll arrive during the warmup match in Paarl, starting on December 28, then the first test in Cape Town on January 2.

His late spell last night showed he's just continuing his form from the 167-run second test win against Sri Lanka in Colombo where he took eight wickets. Helped by two excellent slips catches by Daryl Mitchell, Southee removed Michael Papps and Stephen Murdoch. Then came the big one, Jesse Ryder bowled second ball.